Abbreviations used in the present specification are as follows.
AcNPV: nuclear polyhedrosis virus of Autographa californica 
BG: (1→3)-β-D-glucan
Et: endotoxin (also referred to as lipopolysaccharide)
HEPES: 2-[4-(2-hydroxyethyl)-1-piperazinyl]ethanesulfonic acid
HRP: horseradish peroxidase
MOI: multiplicity of infection
NPV: nuclear polyhedrosis virus
PBS: phosphate buffered saline
PCR: polymerase chain reaction
pNA: p-nitroaniline
PVDF: polyvinylidene difluoride
SDS: sodium dodecyl sulfate
SDS-PAGE: sodium dodecyl sulfate-polyacrylamide gel electrophoresis
Japanese Patent Application laid-Open (kokai) No. 08-122334 and a non-patent document (J. Protein Chem., 5, p. 255-268 (1986)) disclose methods for determining Et or BG by use of an amebocyte lysate of a horseshoe crab (hereinafter referred to simply as a lysate). These methods are based on coagulation of the lysate by Et or BG. The coagulation reaction occurs through cascade reaction of coagulation factors.
For example, when BG is brought into contact with the lysate, factor G contained in the lysate is activated, to thereby form activated factor G. The activated factor G activates a pro-clotting enzyme present in the lysate, to thereby form a clotting enzyme. The clotting enzyme hydrolyzes a specific site of a coagulogen molecule present in the lysate, thereby forming coagulin gel, leading to coagulation of the lysate. The coagulogen also acts on a synthetic substrate (e.g., t-butoxycarbonyl-leucyl-glycyl-arginine-pNA (Boc-Leu-Gly-Arg-pNA)), to thereby hydrolyze the amide bonds, whereby pNA is released. Thus, BG can be determined through measuring absorbance of the formed coloring substance (pNA) (disclosed in Japanese Patent Application laid-Open (kokai) No. 08-122334).
Factor G is a protein formed of subunits α and β, and cloning of each subunit has already been performed (disclosed in J. Biol. Chem., 269(2), p. 1370-1374 (1994)). However, an active protein (factor G) has been difficult to express through employment of cloned DNAs encoding the subunits.